The end of the year saw no letup in cloak and dagger incidents thought to involve Russia, with members of an alleged spy ring in Lithuania arrested on December 31 near the southern base for the NATO air policing mission.

Among those detained on Wednesday in the city of Šiauliai, near NATO's Zokniai air base, was a Lithuanian air force officer who prosecutors said is suspected of spying for a foreign intelligence service and providing it classified information.

Also detained were individuals accused of accepting the information from the officer. The arrests occurred under Article 119 of Lithuania's criminal code pertaining to espionage.

Zokniai has been the main hub for NATO air operations since March 2004, as allied countries have rotated in and out to perform air identification and interdiction missions on behalf of the Baltic states of Estonia, Latvia and Lithuania.

Ämari air base in Estonia, which began hosting NATO planes for the Baltic air patrol in 2014, is officially welcoming pilots and support staff from Spain today. The Spanish will serve a four-month rotation, replacing Germany, which has been based at Ämari since September.

The German contingent made headlines earlier this week when it became public that the pilots' hotel rooms in Tallinn had been broken into several weeks ago during their rotation in Estonia. The incident is under investigation by the Internal Security Service.

In Lithuania, it is the second recent case where prosecutors announced the arrest of suspected spies in strategic locations.

In November, the country detained two individuals, charging them with spying for the intelligence organization of Belarus. One was a paramedic for the armed forces, another worked at a state-run air navigation company.

With the start of 2015, Belgian F-16 fighters have now assumed responsibility for the Baltic air patrol in Lithuania.